noun

• Someone who identifies; a person who establishes the identity of someone or something.
• Something that identifies or uniquely points to something or someone else.
• One who identifies as a particular type or role; one who says and believes that they are a certain thing.
• A guidebook that helps determine the specific class of an object (such as a mushroom, herb, fish, bird, drug, or mineral), or its individual identity (such as that of a star).
• (programming, operating systems) A formal name used in source code to refer to a variable, function, procedure, package, etc. or in an operating system to refer to a process, user, group, etc.
• (HTML) A code that distinguishes a particular element from all other elements in a document.
• (databases) A primary key.